In this work, the first public implementation of the High Efficiency Image File Format was created. The implementation consists of a writer application for creating HEIF files and a reader API which can be used to access the files created. A significant part of this work was setting up and maintaining facilities for continuous integration, and improving code quality. The implementation has already been successfully used to demonstrate the features of HEIF in several contexts including MPEG meetings, and for creating a set of conformance candidate files which are proposed to become official test material.
Evaluation of the work shows that it was possible to improve and maintain sufficient software quality during the project. Several code metrics were extracted from the source code repository version history. The metrics show that eventually the written test cases achieved a high code coverage of over 80%. This did not only mean that most of the code was automatically tested, but it also enabled the extensive dynamic analysis of programs. Several problems were quickly diagnosed and fixed thanks to it. When the violations found by static analysis were related to the amount of code, it can be seen that the frequency of violations decreased and stabilized before the first public release.
The combination of dynamic and static analysis seemed to supplement each other like expected, as static analysis logs were completely free of most serious class find-ings. In order to achieve better code quality it could have been beneficial to inte-grate static analysis into the continuous integration system in an earlier phase of the project, and use more extensive analysis. Static analysis messages about video bitstream parser code should be suppressed so less false alarms would be present. An automatic reporting of quality issues to developers would further enhanced the ef-fectiveness of the analysis. Now the used process did not provide real-time feedback for developers about changes in static analysis results.
Automatic processing of the HEIF and ISOBMFF specifications on the box-structure
6. Conclusion 49 level could be considered, as it seems that manual checking of files by using existing tools and by reading specifications is error-prone. Basic machine-readable repre-sentation of specification structures and parsing it would probably be feasible to implement. This would make it possible to automatically analyze generated HEIF files, and enable a better decoupling of testing and the actual application code.
The HEIF is a very competitive image file format by its features and compression efficiency. However, the extensive feature set might also become a burden if sup-porting it turns out to be impractical, and applications with incomplete feature sets appear and cause compatibility issues which frustrate users. Having said that, the usage of ISOBMFF brands can ease this as they define a minimal player operation and therefore guarantee a minimum set of interoperability.
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APPENDIX A. AN HEIF WRITER EXAMPLE INPUT
Input configuration 1 An example of an HEIF file description for the writer appli-cation in JSON format. Encapsulation type meta makes this a single image item, or an image sequence in case the input bitstream contains several images.